I have an 05 RSTD and it seems to run on 3 cylinders unless I hold the gears to red line ( or at least close to it) before the other cylinder kicks in. The motor smooths out and get a little quieter.
My question is it a carb issue, throttle issue, could one of the carbs not be opening when the throttle is engaged, blocked main/pilot/jet, spark plug?
I'm almost certain it's the front left cylinder, only because it's the coldest of the four pipes after a ride.